We will continue and extend our measurements on the forearm flexion/extension system of normal adult male subjects using our versatile new experimental apparatus, the Programmable Limb Testing System (PLTS). Our goal remains a quantitative characterization of musculoskeletal dynamics and the peripheral manifestations of neural activation for humans in-vivo. Specifically, we will: (1) Conduct a series of "step tests" in which very rapid (20 msec), small (1 to 3 degrees of forearm rotation) displacements are imposed on a subject's forearm. By carefully accounting for inertial effects, the variation of the muscle force as a function of time will be deduced. This experiment, which we have been developing during the past year, can yield much quantitative information on both intrinsic muscular response (unmodified by reflex) and reflex feedback characteristics. The measured mechanical and myoelectric responses will be compared to those we have measured previously in our frequency-response tests. (2) Begin to extend our frequency-response measurements to larger amplitudes of motion (all our tests so far have been confined to small forearm rotations). Ensemble-averaging will be employed to identify higher harmonics in the muscle force, length, and EMG, and on this basis we will attempt to generalize our mathematical model for muscle dynamics beyond the range of small motions. (3) Undertake an evaluation of our newly constructed electrode array/myoprocessor (See Section IV) to determine if this system offers any substantial advantages over more conventional surface EMG measurement schemes for studies of neuro-muscular dynamics.